Sur Burger

• 1 small red onion, halved and thinly sliced
• Salt and pepper
• 1 small jalapeño, trimmed and cut into thin strips
• 1⁄4 cup fresh lime juice
• 3 tablespoons plus 1⁄3 cup extra virgin olive oil
• 1 medium yellow onion, finely chopped
• 9 cloves garlic
• 1⁄2 teaspoon ground cumin
• 1⁄2 teaspoon dried oregano
• 1⁄2 teaspoon cayenne
• 6 ounce cured chorizo, cut in chunks
• 1 pound ground beef chuck
• 3 ancho chiles—torn, seeds and stems discarded
• 1⁄4 cup walnuts
• 8 ounce creamy French feta cheese
• 4 Portuguese rolls, split
• 3 plum tomatoes, sliced
• Romaine lettuce leaves

In a medium bowl, toss the sliced red onion with 1⁄2 tsp. salt. Add hot water just to cover; let stand 3 minutes. Drain the onion and rinse with cold water. Pat dry; transfer to a clean bowl and toss with the jalapeño and lime juice. Let stand at least 30 minutes or up to 4 hours before serving.

Meanwhile, in a medium skillet, heat 2 tbsp. of the extra virgin olive oil over medium. Add the chopped yellow onion and cook until soft, about 5 minutes. Grate 6 of the garlic cloves into the pan; stir in the cumin, oregano, cayenne, 1⁄2 tsp. salt and 1⁄2 tsp. pepper. Cook for 1 minute. Transfer the onion mixture to a large bowl and let cool. Chop the chorizo in a food processor, then add to the bowl with the onion mixture. Reserve the processor bowl. Crumble the ground beef into the onion mixture, and toss gently to combine. Shape mixture into 4 four-inch oval patties and refrigerate.

In a bowl, combine the ancho chile pieces and 2 cups hot tap water; let stand 30 minutes. Reserve 1⁄4 cup of the ancho liquid, then drain chiles and transfer to the food processor. Add the ancho liquid, the remaining 3 cloves garlic and the walnuts and pulse to chop. Add the feta, then, with the motor running, stream in 1⁄3 cup of the extra virgin olive oil, processing until the mixture is the consistency of mayonnaise.

Preheat the broiler, and heat a large cast-iron skillet over medium. Add the remaining 1 tbsp. extra virgin olive oil, then the patties and cook, turning once, about 4 minutes per side.

Meanwhile, broil the rolls, cut sides up, until toasted, about 1 minute. Transfer the rolls to plates, and spread some of the walnut-pepper sauce on each. Place a burger on each roll bottom, then top with tomato slices, romaine, jalapeño-onion relish and the roll tops. Serve with more walnut- pepper sauce on the side.